1. Field of the Invention
The present invention relates to a brush device for a d.c. machine such as a starter motor.
2. Discussion of Background
FIG. 3 is a front view showing a conventional brush device as disclosed, for instance, in U.S. Pat. No. 4,754,184. In FIG. 3, reference numeral 1 designates a commutator for a d.c. machine, numeral 30 designates an insertion opening for receiving the commutator 1, and numeral 2 designates a brush holder of a molded product of a synthetic resinous material wherein four brush boxes 2a having a channel-like shape in cross-section are formed in one side of the brush holder 2. Each top portion in the radial direction of the brush boxes 2a is closed but the inner portion of each of the brush boxes 2a is open, and the front end side of the brush boxes 2a to which an insulating plate 6 (which is described later) is contacted has an open portion 2b. A pair of projections 2d are formed in the brush holder 2 so as to project outwardly. The brush boxes 2a receive brushes 3a of a negative pole and brushes 3b of a positive pole. A brush spring 5 is put in each of the brush boxes 2a so as to push each of the brushes 3a, 3b toward the insertion opening 30.
Numeral 6 designates an insulating plate which is engaged radially with an engaging portion 2c of the brush holder 2 and which closes the opening portion 2b of each of the brush boxes 2a to thereby form brush receiving portions 31. The insulating plate 6 insulates the brushes 3a, 3b from the rear bracket of the d.c. machine.
Numerals 7a, 7b designate a pair of fitting pieces which are fitted to a the pair of projections 2d of the brush holder 2 and push or clamp, for engagement and position-determination, the insulating plate 6 to the brush holder 2. The fitting pieces 7a, 7b are made of metal and are provided with threaded holes so that they are attached to the rear bracket by means of bolts. FIG. 4 shows an embodiment of the fitting piece 7b.
In FIG. 3, reference numeral 7c designates a pair of projections which are formed integrally with the fitting piece 7a and which are connected by welding with lead wires 4a extended from the pair of brushes 3a of a negative pole, whereby the brushes 3a are electrically connected to the rear bracket. Lead wires 4b are extended from the pair of brushes 3b of a positive pole and are electrically connected to a single lead wire 9.
Explanation of the above-mentioned conventional device will be made as to how to attach the brushes 3a, 3b to the brush holder 2.
First, each of the lead wires 4a for the pair of brushes 3a is connected to the fitting piece 7a by means of each of the projections 7c formed integrally with the fitting piece 7a, whereby a brush connector is formed. Before attaching the insulating plate 6, the brush connector is located in the vicinity of the projection 2d which is extended to the left side of the brush holder 2, and then, one of the brushes, e.g. the brush 3a located at the upper part is fitted to the upper left brush box 2a by hand. Pushing the upper brush 3a into the brush box 2a, which is fitted to the brush box 2a so that the brush 3a does not come off the brush box 2a, the fitting piece 7a is moved beyond the projection 2d from the front side to the rear side of the projection 2d so as not to interfere with the projection 2d. In this case, the lower brush 3a which is not yet fitted to the other brush box 2a is in a state of hanging from the fitting piece 7a at the lower side of the projection 2d, which has been moved beyond the projection 2d together with the upper brush 3a. Then, the lower brush 3a is brought to the front side and is fitted to the lower left brush box 2a. Thereafter, each brush spring is put under compression to the top portion of each of the brushes 3a.
Next, the pair of lead wires 4b connected with the brushes 3b and the lead wire 9 are connected to the right fitting piece 7b. In the same manner as the case of the fitting piece 7a, the fitting piece 7b is located in the vicinity of the right projection 2d, and the pair of brushes 3b are successively fitted to the upper and lower right brush boxes 2a.
The insulating plate 6 is brought to the front side of the brush holder 2, and the right and left fitting pieces 7a, 7b are moved radially toward the center of the brush holder 2 to be fitted to the projections 2d. At the same time, the edges of the insulating plate 6 are clamped from the right and left sides by means of the fitting pieces 7a, 7b. In the state that the pair of brushes 3a are fitted to the brush boxes 2a, the brushes 3a can be moved in the radial direction so that there is looseness in the lead wires 4a. Accordingly, it is possible to attach the fitting piece 7a from the left side of the projection 2d.
When the fitting piece 7a is moved from the front side to the rear side of the brush holder 2 after the pair of brushes 3a have been fitted to the brush boxes 2a, there is interference between the fitting piece 7a and the projections 2d, and accordingly, the movement of the fitting piece 7a is impossible. Even though the brushes 3a are moved outwardly in the radial direction, it is impossible to avoid both projections 2d. Since the projections 2d are provided at a position deflected to the front side of the brush holder 2 (in FIG. 1B, the projections 12d are formed at the upper and lower right portions of the brush holder 12), the brushes 3a fitted to the brush boxes 2a are not on the same plane with the fitting piece 7a under a condition that fitting piece 7a is in contact with the projections 2d from the front side, and accordingly, the lead wires 4a are inclined, whereby the length of the lead wires 4a becomes short. On the other hand, in accordance with the above-mentioned method, the brushes 3a fitted to the brush boxes 2a are flush with the fitting piece 7a, and the brushes 3a can be freely movable in the radial direction in the brush boxes 2a, whereby there can be looseness in the lead wires 4a.
However, in the above-mentioned conventional brush device, when the brushes 3a, 3b are put in the brush boxes 2a of the brush holder 2, it is necessary to put them in the brush boxes 2a in the axial direction after the brushes are moved inwardly in the radial direction. Accordingly, automation of assembling the brushes is difficult, and manual operation of such assembling work decreases productivity.